As the material which is swelled and gelled by an absorption of an aqueous substance to a high degree when in contact with the aqueous substance, there may be included synthetic polymeric materials widely used for sanitary cotton, paper diapers, such as starch-acrylonitrile graft polymer hydrolyzates, starch-acrylic acid graft polymer neutralized products, saponified products of vinyl acetate-acrylate copolymers, hydrolyzate of acrylonitrile copolymers or acrylamide copolymers, or self-crosslinked type sodium polyacrylate.
Alternatively, among the substances which can be utilized in many fields, including pharmaceutical and cosmetics, those which cause a swelling and gelling of aqueous substances by an absorption of aqueous substances include natural polymers such as various polysaccharides, gelatin, synthetic polymers such as polyoxyethylene, acrylic acid type polymers, and inorganic mineral substances such as montmorillonite, silica. Particularly, among these, polyacrylic acid type polymers can further enhance the strength when gelled by mixing same with polyvalent oxides, polyvalent hydroxides, organic polyvalent metal compounds and salts thereof, or alumina and silica, as a crosslinking agent, and therefore are actually employed as a base for poultices. When this kind of gel is dried by a known method, when in contact with an aqueous substance, such an aqueous substance may be absorbed to some extent, but the stability and strength of the gel may be inferior with each substance alone, or the composition comprising the above-mentioned polymer and the above-mentioned crosslinking generally have too high a gel strength, whereby sometimes a gel having a sufficient aqueous substance will not be formed.
Emerson (J. Soil Science, 14, 52, 1963) reports that, when several % of a polyacrylic acid is added to a montmorillonite type soil, both form a complex material to become an improved soil which will not be scattered by rain.
In addition to the drawbacks as mentioned above of the composition or the complex material of the prior art, however, when directed to specific uses, for example, the synthetic polymeric materials used for the above-mentioned hygienic cotton and paper diapers probably has impurities such as unreacted monomers, polymerization initiators, crosslinking agents, and surfactants remaining therein, whereby their uses may be sometimes limited due to the characteristics of the starting materials themselves, and it has been difficult to direct them to uses for pharmaceuticals and cosmetics, for which a high safety is particularly demanded.
Also, concerning the substances used frequently for pharmaceutical and cosmetics among the compositions or complex materials as mentioned above, because of a weak gelling force thereof, drawbacks such that they were required to be formulated in large amounts, or that the gels were readily destroyed on account of presence of various salts, occurred.
Further, the complex material of polyacrylic acid and montmorillo-nite type soil reported by Emerson has a problem in that the swelling ability is low because of small content of polyacrylic acid, and the gel strength is extremely weak.